This invention relates to variable amplitude vibratory apparatus, and more particularly to rotational type vibration generating mechanism wherein the vibrational amplitude is a function of rotational velocity.
At the present time, various vibrational devices are in commercial use. These include conveyors, shaker screens, pile drivers, pavement breakers, asphalt finishers, cement spreaders, concrete vibrators, grain crushers, and similar mechanisms. One particular type of vibratory device is a vibratory roller/compactor wherein vibration is utilized in addition to the usual rolling action to effect compaction of the underlying material. In many instances it is considered desirable to vary the vibrational amplitude of such apparatus in order to increase versatility and thereby render the apparatus more useful. For example, in the case of a vibratory roller/compactor it is considered desirable to maintain a large vibrational amplitude when the device is operating at lower vibrational speeds in order to compact coarse materials in deep lifts, and to reduce the vibrational amplitude when the device is operating at higher (rotating) vibrational speeds and working in thin lifts on finely graded material such as asphalt so as not to crush and destroy the material being compacted.
Heretofore changes in vibrational amplitude have typically comprised dual amplitude or multiple amplitude devices. That is, such devices have been capable of vibrating at two or more specific amplitudes, but have not been capable of operating over an infinitely variable range of amplitudes. Thus, a need exists for a variable amplitude vibratory apparatus wherein the vibrational amplitude can be varied over a range, and wherein the vibrational amplitude can be selected to provide the most efficient operation.
Other variable amplitude devices have been developed and are in use in vibratory/roller compactors. However, these devices require elaborate control systems for the transfer of fluids and gases and the restriction of speeds through elaborate electrical controls when the fluid displacement is at a maximum. Thus, the need exists for a variable amplitude vibratory apparatus that does not require special controls or liquid or gas connections to the inside of the drum, and that does not require elaborate electrical controls to limit the vibrational speed.
The present invention comprises a variable amplitude vibratory apparatus which overcomes the foregoing and other disadvantages long since associated with the prior art. In accordance with the broader aspects of the invention, a shaft is mounted for rotation about an axis. The shaft is eccentrically weighted so as to effect vibration upon rotation. Additional weight structure is mounted on the shaft for movement radially outwardly against spring action in response to a centrifugal force caused by rotation of the shaft. At a predetermined rotational velocity the force on the weight overcomes the holding power of the spring. Because of this movement the balance of the shaft is changed, and the vibrational amplitude of the apparatus therefore varies as a function of the rotational velocity of the shaft. The amplitude of the apparatus is simply controlled within predetermined limits by controlling the speed of the shaft.
Various embodiments of the invention are disclosed. Each embodiment can be used in any application where forced vibration performs useful work. In accordance with one embodiment, a single movable weight structure is utilized. The movable weight structure is slidably supported on rods which are secured to the shaft. The rods secure springs which are selected so as to prevent movement of the movable weight structure until the rotational velocity of the shaft reaches a predetermined magnitude. Thereafter the movable weight structure slides outwardly on the rods against the action of the springs, with the positioning of the movable weight structure on the rods being dependent on the rotational velocity of the shaft. As the movable weight structure moves outwardly the vibrational amplitude caused by shaft rotation is progressively diminished.
In accordance with a second embodiment of the invention dual movable weight structures are utilized. The shaft is initially balanced. This feature allows smoother acceleration of the shaft and is advantageous in a vibratory roller/compactor when the shaft is being slowed to a stop, so as to prevent resonance with supporting structure. The first movable weight structure is counter balanced, and is mounted for movement outwardly relative to the axis of rotation of the shaft against spring action when the rotational velocity of the shaft reaches a first predetermined magnitude. At this point the vibrational amplitude of the apparatus is maximized. The second movable weight structure is in turn adapted to begin sliding movement outwardly relative to the axis of rotation of the shaft against spring action when the rotational velocity of the shaft reaches a second, higher magnitude. Outward movement of the second movable weight structure functions to diminish vibrational amplitude as the rotational velocity of the shaft increases. The rotational velocity of the shaft may subsequently be reduced if maximum amplitude is desired and may be reduced further to rebalance the shaft before stopping.
A third embodiment of the invention utilizes leaf springs to resist outward movementof a wieght in response to shaft rotation. Dual leaf spring/weight structures may be utilized in order to provide an apparatus that is balanced at low rotational velocities, that is substantially unbalanced when the rotational velocity of the shaft reaches a first predetermined magnitude, and that is unbalanced to a lesser degree when the rotational velocity of the shaft reaches a second, higher predetermined magnitude.
A fourth embodiment of the invention utilizes torsional springs to resist outward movement of weights in response to shaft rotation. Two pairs of torsional spring/weight structures are mounted for pivotal movement about axes perpendicular to the axis of rotation of the shaft. The apparatus is balanced at low rotational shaft velocities, up to a first predetermined magnitude, but thereafter becomes progressively unbalanced as the rotational shaft velocity reaches a second, higher predetermined magnitude.
In accordance with a fifth embodiment of the invention, multiple movable weight structures are utilized so that the shaft is initially balanced. This feature allows smoother acceleration of the shaft and is also advantageous in a vibratory roller/compactor as the shaft is brought to a stop without causing resonance in the drum/frame system. The shaft remains balanced up to a first predetermined shaft rotational velocity, at which point the primary movable weight structure(s) commences outward movement relative to the axis of rotation of the shaft against spring action. At a second predetermined rotational shaft velocity, the primary movable weight structure reaches maximum outward displacement, whereby the vibrational amplitude of the apparatus is maximized. Outward movement of the secondary movable weight structure(s) functions to diminish vibrational amplitude as the rotational shaft velocity increases beyond a third predetermined magnitude. Thus, the vibrational amplitude of the apparatus may be changed by increasing or decreasing rotational velocity of the shaft.
A sixth embodiment of the invention incorporates triple movable weight structures and is initially balanced. Dual pivotal weight structures pivot outwardly from the shaft in opposition to elastomeric springs after a first predetermined rotational shaft velocity has been attained. The vibrational amplitude of the apparatus is maximized until the rotational velocity of the shaft reaches a second higher value, when outward movement of the secondary movable weight structure(s) functions to decrease vibrational amplitude as the rotational shaft velocity increases further.
In accordance with a seventh embodiment of the invention, dual movable weight structures are utilized so that the shaft is initially unbalanced. The first movable weight structure is mounted for movement outwardly relative to the axis of rotation of the shaft against stacks of elastomeric springs until the rotational shaft velocity reaches a first predetermined magnitude, which corresponds to maximum vibrational amplitude of the apparatus. The second movable weight structure in turn begins outward movement relative to the axis of rotation of the shaft against stacks of elastomeric springs when the rotational shaft velocity reaches a second predetermined magnitude. This functions to decrease vibrational amplitude of the apparatus as the rotational shaft velocity increases.
According to an eighth embodiment of the invention, dual movable weight structures are enclosed within a housing on a shaft so as to be initially balanced. Elastomeric springs are utilized to resist outward movement of the weights in response to shaft rotation. The shaft is balanced until rotational shaft velocity reaches a first predetermined value, at which point the first movable weight structure begins outward movement relative to the axis of rotation of the shaft until reaching a maximum displacement corresponding to maximum vibrational amplitude. At a second, higher predetermined shaft rotational velocity, the second movable weight structure begins outward movement which tends to counterbalance the shaft, decreasing vibrational amplitude as the rotational shaft velocity increases. After the second movable weight structure reaches maximum displacement, the vibrational amplitude stays constant in spite of further increases in rotation shaft velocity. In each of the foregoing embodiments, other spring systems, including elastomeric springs, coil springs, and disc springs, may be utilized interchangeably to resist weight movement, if desired.
The ninth embodiment of the invention features dual movable weight structures constructed of a resilient material so as to resist deflection thereof. The weight structure is enclosed within a housing mounted on a shaft which is balanced. The dual, combination spring/weight structures are responsive to rotational shaft velocity to provide an apparatus that is balanced at relatively low rotational velocity, that is substantially unbalanced when the rotational shaft velocity reaches a first predetermined magnitude, and that is unbalanced to a lesser extent when the rotational shaft velocity reaches a second, higher predetermined magnitude.